Microwave transmission line apparatus having flexibly connected displaceable conductor



June 11, 1968. J. L. BUTLER MICROWAVE TRANSMISSION LINE A 3,388,350PPARATUS HAVING FLEXIBLY, CONNECTED DISPLACEABL-E CONDUCTOR Filed May21, 1965 3 Sheets-Sheet l J. L. BUTLER 3,388,350 MICROWAVE TRANSMISSIONLINE APPARATUS HAVING June 1 1, 1968 FLEXIBLY CONNECTED DISPLACEABLECONDUCTOR 3 Sheets-Sheet Filed May 21, 1965 7% A M W M ll Q firm l wl Il 1| MM i ,M Q a0 0 0 l y w L IN: W W 0 :MH l x I. Va ll 1A i I 1 w w A;fl 7 w W #4 M W m M W 0 Md Mg June 11, 1968 J. BUTLER 3,388,350

MICROWAVE TRANSMISSION LINE APPARATUS HAVING FLEXIBLY CONNECTEDDISPLACEABLE CONDUCTOR Filed May 21, 1965 5 Sheets-Sheet 3 M w W W M T!A! 0% "1 p/ United States Patent 01 MICRQWAVE TRANSMHSSEON LINEAPPARATUS HAVING FLEXIBLY CONNECTED DlSlLAfiE- ABLE CONDUCTGR Jesse L.Butler, Groton Road, RED. 2, Nashua, N.H. @3060 Filed May 21, 1965, Ser.No. 457,570 16 Claims. (Cl. 333) ABSTRACT OF THE DISCLOSURE Anadjustable transmission line component includes a casing that definestwo outer conductor ground planes and on which are supported twoterminal structures between which an inner conductor extends. The innerconductor includes a rigid control section that is connected to theterminals by two flexible slab line sections, each of which isrelatively rigid in the vertical plane and relatively flexible in thehorizontal plane. The spacing of the outer conductors and the amount ofdielectric material change in a transition region. The central portionof the inner conductor is moved an adjusting screw through thetransition region to change the velocity of propagation of the signalapplied at the terminals through the component, thereby producing aphase shift.

This invention relates to electrical transmission line apparatus andmore particularly to adjustable apparatus for varying a signal appliedto an electrical transmission line.

It is frequently desirable to shift the phase of an electrical signalthat is to be applied to an electrical transmission line. In electricaltransmission systems which operate at microwave frequencies, such phaseshifts have been accomplished generally by the use of a trombone linestretcher in which transmission line conductors are coupled togetherwith sliding connections so that the actual mechanical length of theline can be varied; or by the movement of a block of dielectric materialin a transverse direction relative to the transmission line between aregion of relatively weak field strength and a region of relativelystrong field strength, e.g., from one side of the transmission lineinwardly towards the center of the transmission line. This inward motioneffects a reduction in the wave length of the transmission line and,thus, a corresponding change in its electrical length, which produces aphase shift, but also produces a change in the impedance of thetransmission line as the dielectric member is moved closer to the centerof the transmission line.

Accordingly, it is an object of this invention to provide novel andimproved high frequency electrical apparatus for varying thecharacteristics of an electrical signal.

Another object of the invention is to provide a novel and improvedtransmission line phase shifter.

Another object of the invention is to provide transmission lineapparatus in which a given electromagnetic characteristic, such as thevelocity of propagation of the transmitted wave, can be selectivelyadjusted without necessarily affecting other electromagneticcharacteristics of the apparatus, such as its characteristic impedance.

Another object of the invention is to provide adjustable transmissionline apparatus, suitable for producing a predetermined phase shift inthe transmitted wave, which is accurately and easily adjustable,reliable, and inexpensive to manufacture. j

A further object of the invention is to provide such an adjustablecomponent in the form of a variable directional coupler.

In accordance with the invention there is provided high frequencyelectrical transmission line apparatus comprisice ing a pair of spacedouter conductors with dielectric material disposed between the outerconductors. A third relatively narrow center conductor is locatedbetween and equidistant from the pair of outer conductors and includes arigid center portion that is adapted to be moved through a transitionregion relative to the two outer conductors while maintaining itsequidistant position with respect to those two outer conductors. Thiscentral portion of the center conductor is connected to fixed terminalstructures by slab line connecting links which are thin in the plane ofmotion of the central portion and hence easily flexed in that plane.

In addition, the characteristics of the transmission line apparatuschange in the transition region. The dielectric material disposed inthat region may have an electrically significant parameter that variesalong the range of positions of the movable central conductor portion,and/or the spacing of the pair of outer conductors in the transitionregion may vary. For example, the outer conductor spacing may change ina manner related to the variation of the dielectric material parameterso that the characteristic impedance of the apparatus is independent ofthe position of the movable central conductor portion throughout saidtransition region. The invention provides appa ratus in which thevelocity of propagation along a transmission line, attenuation ofelectrical signal, or the characteristic impedance of the apparatus maybe controlled without sliding metallic or capacitive connections. Theinvention may be incorporated in a variety of apparatus, including phaseshifters and directional couplers.

Other objects, features and advantages of the invention will be seen asthe following description of the particular embodiments of the inventionprogresses, in conjunction with the drawings in which:

FIG. 1 is a diagrammatic perspective view of a transmission lineapparatus constructed in accordance with the invention;

FIG. 2 is a diagrammatic plan view with parts broken away, of theapparatus shown in FIG. 1;

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 2;

PIGSQ4 and 5 are diagrammatic plan views of two other embodiments of theinvention;

FIG. 6 is a diagrammatic plan view, with parts broken away, of stillanother embodiment of the invention;

FIG. 7 is a sectional view taken along the line 77 of FIG. 6;

FIG. 8 is a diagrammatic plan view of a directional coupler constructedin accordance with the invention; and

FIG. 9 is a sectional view taken along the line 9-9 of FIG. 8.

Referring to the drawings, one embodiment of the invention is shown inFIGS. 1-3. This embodiment generally comprises two spaced outerconductors 1t 11 and an inner conductor 13 disposed equidistantlybetween the two outer conductors. The apparatus has a casing which iscompleted by end members 15, 16 on which terminal structures 20, 22 aresupported and side members 17, 18 which connect the two outer conductors10, 11 together.

Center conductor 13 comprises a rigid movable central portion 25 withsubstantially flexible slab line portions 27, 29 connecting centralportion 25 to terminals 24}, 22. Each conductor portion 27, 29 isrelatively rigid in the vertical plane and relatively flexible in thehorizontal plane. By adjustment of the vertical height of portions 27,29 with respect to the spacing of the outer conductors 10, 11, adjacentthose portions, the characteristic impedance characteristics of thetransmission line in the regions of the flexible and rigid sections ofthe center conductor 13 can be made the same. Two dielectric guide rails35, 36 extend between side walls 17, 18 transverse to the direction ofsignal transmission. Rigid central portion is slidingly supported uponrails 35, 36 for transverse motion. Adjusting screw 40 bears againstmoveable portion 25 and spring 37 biases the movable portion 25 intoengagement with screw 40. By virtue of this arrangement, the movableconductor portion 25 can, through rotation of screw 40, be shiftedthrough a continuous range of positions extending transverse to thedirection of signal transmission through the line component betweenterminals 26 and 22. This range of positions is defined herein as atransition region.

Outer conductors 10 and 11, in the transition region,

comprise planar segments 45, 46, 47, a, 46a, and 4711.

As indicated in FIG. 3, segments 45 and 450 are parallel to one another;segments 47 and 4711 are also parallel to one another but spaced agreater distance apart; and segments 46 and 4612 are transition memberswhich slant away from one another towards segments 47 and 47a. Inclinedtransition segments 48 connect segments 46 and 47 with the base planarsegment 45. It will be noted that the corresponding opposing segments ofthe two Outer conductors 19, 11 are arranged symmetrically with respectto movable central conductor portion 25, so that, as portion 25 movesthrough its range of positions, it is always midway between the outerconductors.

Thus, parallel segments 45, 45a define a region of relatively smallouter conductor spacing; parallel segments 47, 47a define a region ofrelatively large outer conductor spacing; and transitional non-parallelsegments 46, 46a define a transition region of gradually increasing(from left to right in FIG. 3) spacing.

Solid dielectric material is disposed on the inner surfaces ofconductors 10 and 11 in a manner so that an electrically significantparameter of the dielectric varies in the direction of motion of centralconductor portion 25 in compensation for the variation in outerconductor spacing so that the transmission line component has a uniformcharacteristic impedance which is independent of the position of movableconductor portion 25 within the transition region. The appropriatecontour of the ground planes 1t) and 11 may be designed on a point bypoint basis with respect to static measurements of the capacitance ofthe device. In the embodiment shown, the material 50 has a uniformdielectric constant and the variable parameter is the thickness of thatmaterial which is zero between segments 45, 45a, and increases uniformlyin a wedge-shaped form along segments 46, 46a, until it reaches segments47, 470 along which it continues in uniform thickness.

In operation, when the component is connected into a transmission systemby means of terminals 20, 22, the velocity of propagation of the signalthrough the component can be changed simply by adjusting the position ofmovable central conductor portion 25, thereby producing a phase shift inthe transmitted wave signal. Adjusted positions of movable portion 25are shown in dotted lines in FIG. 2.

Apparatus constructed in accordance with the invention may take avariety of forms. In the embodiment shown in FIG. 4, a rigid movableportion 25 is folded back upon itself several times in serpentinefashion, thus increasing the length of the center conductor disposed inthe transition region of variable propagational velocity. It will benoted that the length of portion 25' is several times the length of theouter conductors adjacent that region. In this manner, a larger phaseshift may be produced for a given movement of portion 25'. Dielectricscrew 40 is used to adjust the position of conductor portion 25'. In theembodiment shown in FIG. 5, a dielectric cord 40" is attached to movableportion 25" and extends between side walls 17", 18" to the exterior ofthe component. Adjustment is obtained by movement of cord 40".

FIGS. 6 and 7 show still another embodiment of phase shifter having acasing 100 that includes outer conductors or ground planes 102, 104connected by side walls 106,

108 and end walls 110, 112. Disposed on side wall 106 is terminalstructure 114 and disposed on side wall 108 is terminal structure 116. Acenter conductor 118 extends between terminals 114, 116. That centerconductor includes flexible slab line portions 126, 122 and twosuperimposed serpentine segments 124, 126 that are secured on oppositeside of dielectric support sheet 128. Tapered transition sections 129connect slab line portions 120, 122 with segments 124, 126 in mannersimilar to corresponding transition sections employed in theabove-described embodiments. Segments 124, 126 may be thin copper foilmembers that are deposited or laminated on sheet 128 by printed circuittechniques. Support 128 is disposed for sliding movement in tracks orgrooves 130 formed in side walls 106, 188. Springs 131 bias support 128to the right against micrometer screw structure 132. Adjustment of screwstructure 132 moves sheet 128 and conductor segments 124, 126 betweenthe ground plane conductors 1G2, 104.

As indicated in FIG. 7 each ground plane includes a section 134 ofsubstantial thickness and a relatively thin section 136. The abrupttransition between the two sections is the transition region. Secured toeach thin section 136 is a dielectric block 138 of uniform thickness anduniform dielectric constant. It will be noted that in the region ofincreased spacing between ground plane conductors 102, 104, dielectricmaterial 138 is inserted. The amount and characteristic of dielectricmaterial is selected so that the characteristic impedance does notchange between sections 134 and 136. The relation, to a first orderapproximation, is d /d =k /k where d is the spacing between ground planesections 134, d is the spacing between ground plane sections 136, k isthe dielectric constant between sections 134; and k is the dielectricconstant between sections 136.

The velocity of propagation however is inversely proportional to thesquare root of the dielectric constant but independent of the groundplane spacing. Thus, when sheet 128 is slid in grooves 130 theproportion of center conductor segments 124, 126 in the dielectricloaded region changes and, as a result, the signal transit times fromterminal 114 to terminal .116 changes and accordingly, a phase shift isproduced. It will be seen that a similar analysis is equally applicablewith respect to the embodiments shown in FIGS. 1-5.

FIGS. 8 and 9 show the application of the invention to a variabledirectional coupler. Two separately suspended inner conductors 150, 152,are disposed between ground plane conductors 154, 156. Each innerconductor includes two flexible slab line portions 158 and a rigidcenter portion 160. The inner conductors extend between terminals 162and 164 which are secured to side wall portions 166, 168 of the couplerhousing. Each ground plane 154, 156 includes two fiat sections 170, 172and a transition section 174. Dielectric rod 176 which passes throughside wall 178 has threaded sections 180, 182 of different pitch. Section180 is threadedly engaged at side wall 178 while section 182 isthreadedly engaged to block 184 which is ecured to conductor 150. Rod176 has a reduced portion at that point that it passes through block 186(secured to conductor 152) and is free to rotate relative thereto. Thus,when rod 176 is rotated, conductor portions 160, can be caused to movecloser together as they simultaneously moved into a region of increasedgroundplane spacing. This modifies the relative characteristic impedanceof the two transmission lines and thus modifies the response of thedirectional coupler.

While particular embodiments of the invention have been shown anddescribed, additional modifications will be obvious to those skilled inthe art. For example, if a lossy dielectric is employed in thetransition region, a variable attenuator device results. Also, it isobvious that the movable center conductor portion, rather thantraversing the transition region with straight line motion, may movealong other paths such as pivoting about some actual or virtual point.Therefore, it will be understood that the invention is not limited tothe disclosed embodiments or to details thereof and departures may bemade therefrom within the spirit and scope of the invention as definedin the claims.

What is claimed is:

1. High frequency electrical transmission line apparatus comprising:

a pair of spaced outer conductors,

dielectric material disposed between said outer conductors,

at least one electrically significant parameter of said dielectricmaterial that affects velocity of propagation changing at a transitionregion,

at least one inner conductor narrower than and located between saidouter conductors, said inner conductor having a fixed terminal, amovable portion adapted to be moved through said transition regionrelative to said outer conductors and at least one flexible portionconnecting said movable portion to said fixed terminal,

and means for moving said movable portion through said transitionregion.

2. The apparatus of claim 1 wherein said flexible portion is ofrectangular cross-sectional configuration and is relatively flexible inthe direction of motion of said movable portion across said transitionregion while being relatively rigid in the plane perpendicular thereto.

3. The apparatus as claimed in claim 1 wherein the spacing of said outerconductors changes at said transition region.

4. The apparatus as claimed in claim 1 wherein the dielectric constantof said dielectric material between said outer conductors changes atsaid transition region.

'5. The apparatus as claimed in claim 1 wherein both the spacing of saidouter conductors and the dielectric constant of said dielectric materialchanges at said transition region.

6. The apparatus as claimed in claim 1 wherein the spacing of said outerconductors increases at said transition region and the dielectricconstant of said dielectric material changes proportionally in theregion of increased outer conductor spacing so that the characteristicimpedanoe of said apparatus is not varied due to the transition region.

7. The apparatus of claim 1 wherein said movable portion is folded backupon itself at least once, thereby providing a movable portion of innerconductor substantially longer than the length of said outer conductorsin said transition region.

8. The apparatus of claim 1 wherein the apparatus includes two innerconductors, each having a fixed terminal, a movable portion, and aflexible portion connecting said movable portion to said fixed terminal,said movable portion being adjacent one another for transferringelectrical energy from one inner conductor to the other, and means formoving said movable portions relative to each other and to said outerconductors in said transition region.

9. The apparatus of claim 8 wherein said means for moving said movableportions comprises .a screw threadedly supported relative to said outerconductors, said screw being threaded through at least one of saidmovable portions so that rotation of the screw causes said movableportions to move relative to each other and to said outer conductors.

10. High frequency electrical transmission line apparatus comprising:

a pair of spaced outer conductors,

dielectric material disposed between said outer conductors,

at least one inner conductor narrower than and located between andequidistantly from said outer conductors, said inner conductor having amovable portion adapted to be moved through a transition region relativeto said outer conductors while preserving its equidistant position, afixed terminal, and a flexible portion connecting said movable portionto said fixed terminal,

at least one electrically significant parameter of said dielectricmaterial adjacent said movable portion that affects velocity ofpropagation varying in said transition region, the spacing of said outerconductors adjacent said movable portion varying in a manner related tosaid variance of the dielectric material parameter so that thecharacteristic impedance of the component is independent of the positionof vsaid movable portion in said transition region,

and means for moving said movable portion in said transition region.

11. The apparatus as claimed in claim 10 wherein said outer conductorspacing changes gradually in said transition region.

12. High frequency electrical transmission line apparatus comprising:

a pair of spaced outer conductors each formed of a plurality of planarsegments, extending longitudinally along the direction of transmission,with the transition region being defined between said segments, one pairof segments being spaced farther apart than a second pair of saidsegments,

solid dielectric material disposed between said outer conductors uponthe inner surfaces thereof in the region of greater conduct-or spacing,

at least one inner conductor narrower than and located between andequidistantly from said outer conductors, said inner conductor having arigid movable portion adapted to be moved through a range of positionsrelative to said outer conductors while preserving its equidistantlocation, a fixed terminal, and a flexible portion connecting saidmovable portion to said fixed terminal,

the thickness of said solid dielectric material adjacent said movableportion being related to the spacing of said segments of said outerconductors so that the characteristic impedance of the apparatus isindependent of the position of said movable portion in said transitionregion,

and means for moving said movable portion through said transitionregion.

13. The apparatus of claim 12- wherein said flexible portion is ofrectangular cross-sectional configuration and is relatively flexible inthe direction of motion of said movable portion across said transitionregion while being relatively rigid in the plane perpendicular thereto.

14. High frequency electrical transmission line apparatus comprising:

a pair of spaced outer conductors extending between spaced terminalmeans,

dielectric material disposed between said outer conductors,

at least one electrically significant parameter of said dielectricmaterial that affects velocity of propagation changing at a transitionregion,

a third conductor disposed equidistantly between said pair of outerconductors and extending between said terminal means,

said third conductor including a first portion disposed adjacent saidtransition region and a flexible coupling portion for connecting saidfirst portion to said terminal means,

and means for moving said first portion through said transition regionwhile maintaining said first portion equidistant from said outerconductors,

said coupling portion being of generally rectangular configuration andhaving a dimension in the plane of movement of said first portionsubstantially less than its dimension in the plane perpendicular to saidplane of movement.

15. High frequency electrical transmission line apparatus comprising:

a pair of spaced outer conductors extending between spaced terminalmeans,

dielectric material disposed between said outer conductors,

said outer conductors being spaced apart a first distance at one pointand a second distance at a second point so that a transition region isprovided between said first and second points,

the dielectric constant of said dielectric material at said first andsecond points being related to the spacing between said outer conductorsat those points so that the characteristic impedance of said apparatusis the same at said first and second points,

a third conductor disposed equidistantly between said pair of outerconductors and extending between said terminal means,

said third conductor including a first portion disposed adjacent saidtransition region and a flexible coupling portion for connecting saidfirst portion to said terminal means,

and means for moving said first portion through said transition regionwhile maintaining said first portion equidistant from said outerconductors,

said coupling portion being of generally rectangular configuration andhaving a dimension in the plane 25 of movement of said first portionsubstantially less than its dimension in the plane perpendicular to saidplane of movement.

16. A directional coupler comprising:

a pair of spaced outer conductors extending between two pairs of spacedterminal means,

dielectric material disposed between said outer conductors,

at least one electrically significant parameter of said dielectricmaterial that affects velocity of propagation changing at a transitionregion between said outer conductors,

third and fourth conductor means disposed equidistantly between saidpair of outer conductors and extending between said terminal means,

each of said third and fourth conductor means including a first portiondisposed adjacent said transition region and a flexible coupling portionfor connecting said first portion to said terminal means,

and means for moving said first portions through said transition regionand simultaneously changing the spacing between said first portionswhile maintaining said first portions equidistant from said outerconductors,

each said coupling portion being of generally rectangular configurationand having a dimension in the plane of movement of said first portionsubstantially less than its dimension in the plane perpendicular to saidplane of movement.

References Cited UNITED STATES PATENTS 2,402,624 6/1946 Himmel 333313,005,168 10/1959 Fye 33384 3,013,227 12/1961 Jordan 333-84 30 HERMANKARL SAALBACH, Primary Examiner.

ELI LIEBERMAN, Examiner.

M. L. NUSSBAUM, Assistant Examiner.

